Nextcloud Calendar attachments of local files are offered to downloaded
CVE-2025-66550

5.7MEDIUM

Key Information:

Vendor

Nextcloud
Status
Security-advisories
Vendor
CVE Published:
5 December 2025

What is CVE-2025-66550?

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.

Affected Version(s)

security-advisories >= 5.0.0-rc.1, < 5.2.4 < 5.0.0-rc.1, 5.2.4

security-advisories < 4.7.17 < 4.7.17

References

https://github.com/nextcloud/security-advisories/security...
x_refsource_CONFIRM
https://github.com/nextcloud/calendar/pull/6971
x_refsource_MISC
https://github.com/nextcloud/calendar/commit/63a6c398db01...
x_refsource_MISC

CVSS V3.1

Score:
5.7
Severity:
MEDIUM
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

JSON
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CVE-2025-66550 : Improper Download Verification in Nextcloud Calendar App